dHvA measurements of high-T_c oxides with steady high-magnetic fields

The de Haas-van Alphen (dHvA) effect has been measured in YBa₂Cu₃O₇ (Y123) and Tl₂Ba₂CuO_6+δ (T12201) with oriented-powder samples in H//c-axis direction at the temperature range between 1.6 and 4.2 K with steady high magnetic fields up to 27 T. The oscillatory magnetization was detected by a modulation technique. We performed spectral analysis by employing the maximum entropy method (MEM). In Y123, the spectral density shows apeak at 456 T which corresponds to an extremal cross-section of 0.044 A^-2. The dingle temperature was evaluated to be 7 K using the effective-mass-value of 2.1m_c. In T12201, the maximum of spectral density appeared at 400 T not only for superconducting sample (δ ≅ .08) but also for metallic non-superconducting sample (δ = .1).